Some embodiments described herein relate generally to methods and apparatus for monitoring and controlling the performance of optical communication systems. In particular, but not by way of limitation, some embodiments described herein relate to methods and apparatus for detecting metric values related to the extinction ratio and performing corrections in optical communication systems based on the same.
The extinction ratio (ER) of an optical communication system that includes an optical source (or optical transmitter) and an optical detector (or optical receiver) is the ratio of two optical power levels of a digital signal generated by an optical source such as, for example, a laser diode or an external modulator. One of the two optical power levels is the average optical power level generated when the optical source is in a first configuration (e.g., an “on” configuration that denotes a binary “1” power level). The other of the two optical power levels is the average optical power level generated when the optical source is in a second configuration (e.g., an “off” configuration that denotes a binary “0” power level). The system performance of an optical communication system can be considered as a function of the ER. Therefore, detecting, monitoring and controlling the ER can enhance the performance of optical communication systems such as, for example, high speed communication systems.
Known methods of detecting the ER of an optical communication system typically involves implementing a high bandwidth sampling technique (where the sampling rate is at least equal to or greater than the bit rate of the optical signal to be measured), uses an oscilloscope with synchronous sampling (i.e., using a repetitive “clock” signal generated at the optical source or recovered from the oscilloscope input) to establish the temporal location of the binary “0” power level and the binary “1” power level. This location is called the “center of the eye”. Once the “center of the eye” is located, the power level of the binary “0” and the binary “1” can be measured, and thus ER can be calculated.
Such known methods of detecting the ER of an optical communication system are typically cumbersome. Additionally, synchronous ER detection is typically implemented using high bandwidth electronics (e.g., a piece of test equipment), which are typically costly and typically use a large amount of space.
Accordingly, a need exists for methods and apparatus to measure, monitor and control the performance of an optical communication system using asynchronous detection that do not use a “clock” signal and high bandwidth electronics for sampling optical signals of the optical communication system.